Gaskets

ABSTRACT

A gasket is described. The gasket comprises a sealing layer and a support layer. The sealing layer is formed from a resilient material which comprises a CEV component in a proportion of at least 25% w/w of the sealing layer. The CEV component is at least partially derived from dry CEV. A hydrolysis resistant polymer to improve the water resistance of the sealing layer is also provided in the proportion of less than 20% w/w of the sealing layer. Generally, the level of CEV falls within the range 25-80% w/w of the sealing layer. A method of producing a gasket is also described. The method involves applying a wet sealing layer dough to a support material, and drying the wet sealing layer dough on the support material. The solids content of the wet sealing layer dough prior to the drying step is in the range 30-80% w/w of the dough material.

The present invention is concerned with gaskets, in particular withgaskets having a sealing layer with enhanced properties which is basedupon chemically exfoliated vermiculite.

Exfoliated vermiculite is a known heat-resistant resilient material.Exfoliated vermiculite is conventionally formed by expanding mineralvermiculite using gas, this material being referred to herein as“gas-exfoliated vermiculite”. The gas may be thermally generated, inwhich case the product is called “thermally-exfoliated vermiculite”(TEV). TEV may be made by flash-heating mineral vermiculite to 750-1000°C., at which temperature the water (free and combined) in the orevaporises rapidly and the steam generated forces apart the silicatesheets which form the raw material, so bringing about an expansion of10-20 times perpendicular to the plane of the sheet. The granules formedhave a chemical composition which (apart from the loss of water) isvirtually identical to that of the raw material. Gas-exfoliatedvermiculite may also be made by treating raw vermiculite with a liquidchemical, eg hydrogen peroxide, that penetrates between the silicatesheets and subsequently evolves a gas, eg oxygen, to bring aboutexfoliation.

A different form of exfoliated vermiculite is known as“chemically-exfoliated vermiculite” (CEV) and is formed by treating theore and swelling it in water. In one possible preparation method, theore is treated with saturated sodium chloride solution to exchangemagnesium ions for sodium ions, and then with n-butyl ammonium chlorideto replace sodium ions with n—C₄—H₉NH₃ ions. On washing with waterswelling takes place. The swollen material is then subjected to highshear to produce an aqueous suspension of very fine (diameter below 50μm) vermiculite particles.

It is known to utilise exfoliated vermiculite as a layer of a sheetgasket, eg an automotive head gasket, and for other purposes. Forexample, GB 2 193 953 B discloses forming sheet-like gaskets formed fromparticles of gas-exfoliated vermiculite. Because such particles do notcohere well, they are bound together by fine particles of CEV. The useof CEV as a binder retains heat resistance and resilience, whereas theuse of other inorganic binders could result in an incompressiblestructure. However, although exfoliated vermiculite has excellent heatresistance and a high degree of resilience, it has poor waterresistance. Furthermore, such products were manufactured using CEV witha high water content at low solids content and considerable dryingproblems are encountered during production due to the tendency of CEVcontaining materials to form a surface which prevents the further escapeof moisture.

GB 2 123 034 B describes making a flexible sheet material, eg for agasket, by subjecting an aqueous suspension to electrophoresis. Thesuspension contains an expanded layer silicate, eg CEV with a particlesize below 50 μm, and a dispersed organic polymeric material, eg acrylicpolymer, acrylonitrile-butadiene copolymer, epoxy resin, or naturalrubber. However, high levels of polymer are disclosed to effectsufficient hydrolysis resistance and such levels of polymer givegasketing problems due to a loss of stress retention and gasket creep inuse.

A sealing element for a gasket for the exhaust system of an internalcombustion engine is disclosed in GB 2 217 742 A. This sealing elementcomprises relatively coarse particles of TEV (passing a 2 mm sieve)bonded together by fine CEV particles (about 100 μm in size). Thiselement is stated to disintegrate quickly if exposed to water as thefine CEV particles are readily dispersed in water. In order to improvewater-resistance, GB 2 217 742 A proposes bringing the element intocontact with a solution of an aluminate or a zirconyl salt. Furtherimprovement is achieved by treatment with a solution of a siliconeelastomer. An example is given of impregnation of a sheet (which hadalready been treated with sodium aluminate) by a 15% solution ofsilicone elastomer is toluene, the solids uptake being 3% by weight.However, the product components suffer from a low solids content whichresult in gasketing materials which are difficult to dry. Furthermore,the strength of the components is insufficient for some applicationsboth in terms of processing and water resistance. Numerous attempts havebeen made to solve this problem.

GB 2122699A discloses the use of electrophoresis to remove water fromthe product during production but it is noted that in examples 1 and 2pure vermiculite is deposited on a metal plate but such products werenot boiling water resistant.

U.S. Pat. No. 4,677,551 (Hercules) is directed to ionic bonding usingonium ions of CEV. It describes mixing CEV with polymers and indicatesthat large quantities of organic materials are necessary to introducesufficient binding properties into the CEV and that such largequantities are unsatisfactory. The document is directed to improving thebinding properties using the onium ions.

U.S. Pat. No. 4,762,643 (Armstrong) is directed to improving theproperties of CEV by further treatment using guanidine. In addition, theguanidine derived product is further strengthened using fibres. Example12 of the said document discloses a high level of latex (42%) in orderto impart sufficient binding properties of the CEV. Such high levels oflatex cause a loss in stress retention and high creep in the finalproduct. Such properties are generally unacceptable in gaskets.

U.S. Pat. No. 4,655,482 is directed to improving the properties ofvermiculite dispersions by the use of citrate anions. The citrate anionsfunction as swelling agents for the vermiculite and enhance the rate andextent of swelling to an aqueous medium. The swollen vermiculite isusually delaminated by shearing to provide the inventive dispersions,which comprise a suspension of the delaminated platelets and citrateanions.

It is an object of the present invention to provide a gasket comprisinga sealing layer with improved water resistance. It is a further objectof the present invention to provide a gasket with a sealing layer withreduced loss in stress retention and low creep.

According to a first aspect of the present invention there is provided agasket comprising a sealing layer and a support layer, the sealing layerbeing formed from a resilient material which comprises a CEV componentin a proportion of at least 25% w/w of the sealing layer, the said CEVcomponent being at least partially derived from dry CEV, and ahydrolysis resistant polymer to improve the water resistance of saidsealing layer wherein the proportion of the said polymer does not exceed20% w/w of the sealing layer.

For the avoidance of doubt, a gasket of the present invention mayprovide conventional sealing between static parts and sealing betweenmoving parts such as valves where sealing is only requiredintermittently. An example of the latter would be valve stem sealing.

Preferably, the proportion of CEV is at least 25% w/w of the sealinglayer, more preferably at least 35% w/w of the sealing layer.

Typically, the level of CEV falls within the range 25-80% w/w of thesealing layer, more typically, 30-75% w/w of the sealing layer, mosttypically 35-70% w/w of the sealing layer.

Preferably, the proportion of the said polymer is less than 15% w/w ofthe sealing layer, more preferably, less than 10% w/w. Especiallypreferred is a level of polymer less than 7.5% w/w, more especiallypreferred is a level of polymer in the range 2.0-7.5% w/w of the sealinglayer.

The known prior art products contain high levels of hydrolysis resistantpolymer as, hitherto, such high levels were required in order to providethe level of hydrolysis resistance required. Unfortunately, such levelsof polymer resulted in a loss of stress retention and unsatisfactorylevels of creep, in use. By the use of dry CEV particles in the wetdough composition, it has been surprisingly discovered that much lowerlevels of hydrolysis resistant polymer can be utilised whilst stillproviding the necessary levels of hydrolysis resistance. Such low levelsof hydrolysis resistant polymer cause an increase in stress retentionand reduce the levels of creep in the gasket, in use.

Advantageously, the invention uses higher levels of CEV than hadhitherto been thought possible without encountering drying problemsduring production. Low levels of CEV have been preferred due to thesedrying problems associated with known relatively high water content CEVmaterials. Furthermore, CEV containing materials tend to ‘skin’ easilyduring the drying process ie the surface layer dries to form a skinwhich hinders the escape of further moisture from within the bed of thesealing layer.

Accordingly, preferably, the chemically exfoliated vermiculite componentof the present invention includes sufficient dry CEV, to provide a wetsealing layer dough with a reduced water content which is capable ofbeing dried before substantial skinning has occurred.

The term hydrolysis resistant polymer includes any suitable elastomersuch as silicon and carbon based elastomeric polymers. Suitable polymersfor use with the present invention include:

nitrile butadiene rubbers, styrene butadiene rubbers, natural rubber,butyl rubber, siloxanes (particularly organosiloxanes such as dialkylsiloxanes) and ethylene-propyldiene monomer. Diene-based polymers aresuitable because they are flexible and hydrolysis-resistant.

The support layer may be made of any suitable support material ontowhich the sealing layer may be coated or otherwise deposited to form thegasket. Suitable support layer materials include stainless steel andcarbon steel which may both be in the form of solid metal cores or thinsheets. The solid metal cores may be suitably profiled or machined toreceive the sealing layer. The thin sheets may be in the form of solidsheets, tanged sheet or perforated sheet. Tanged sheet is especiallypreferred. Other suitable support materials include:

wire mesh, such as expanded metal and woven gauze; fibre mesh, such asglass fiber mesh; cloth; or a non woven material, such as tissue.

In the case of leakable materials such as fibre mesh, cloth or tissue,it is particularly advantageous to add the sealing layer in two stages.Firstly, a high solids content filler body is added to the supportmaterial. The filler body is designed to fill the interstices of thesupport material and is, preferably, a high CEV content filler material.A typical filler for such purposes may contain more than 50% CEV,(preferably comprising slurry CEV and PCEV), preferably more than 75%CEV, most preferably more than 95% CEV as the filler material. Afterdrying of the first sealing layer, a second sealing layer is added inaccordance with the composition of the first aspect of the invention.The second layer is subsequently dried and, if necessary, the processrepeated on the reverse side of the support material.

The sealing layer may be mechanically bonded to the support layer, eg bytangs projecting from the support layer into the sealing layer.

The sealing layer of the gasket of the present invention issubstantially water resistant. Preferably, the sealing layer is waterresistant to the extent that it can withstand submersion in boilingwater for a period in excess of 2 hours, more preferably, in excess of 5hours, most preferably, in excess of 7 hours. Preferably, the product issubstantially ambient water resistant, where ambient water resistancemay be taken to mean a sealing layer which can withstand submersion inambient water with or without agitation of the sealing layer for aperiod in excess of 20 hours, more preferably 20 days, most preferably200 days.

According to a second aspect of the present invention there is provideda method of producing a gasket in accordance with the first aspect ofthe invention involving the steps of:

(a) the application of a wet sealing layer dough to a support material,and

(b) drying the said wet sealing layer dough on the support material.

wherein the solids content of the wet sealing layer dough prior to thedrying step is in the range 30-80% w/w of the dough material.

Preferably, the solids content of the said dough is in the range 35-70%w/w of the wet dough material, more preferably, 40-65% w/w of the wetdough material, most preferably, 45-60% w/w of the wet dough material.

Preferably, in accordance with any aspect of the present invention theCEV is mixed with a suitable filling agent such as thermally exfoliatedvermiculite (TEV). Preferably, the filling agent comprises less than 75%w/w of the sealing layer, more preferably, less than 70% w/w, mostpreferably, less than 65% w/w of the sealing layer. In many cases theTEV content in the dough is less than 55% w/w. Preferably, the fillingagent is a plate-like filler.

Preferably, a wet sealing layer dough in accordance with the presentinvention may be dried within 4.0 hours/side/mm dry thickness, morepreferably, 3.0 hours/side/mm dry thickness, most preferably, 2.5hours/side/mm dry thickness.

A dough in accordance with the present invention may be dried between80-135° C., more preferably, 100-130° C., most preferably, 115-125° C.

Preferably, the relative ratio of non-dry derived CEV to dry CEV in thedried sealing layer component is between 0.01:1 and 20:1, morepreferably between 0.05:1 and 10:1, most preferably between 0.1:1 and4:1.

Since CEV is a relatively expensive material compared withgas-exfoliated vermiculite, eg TEV, in a gasket according to theinvention, the resilient layer may also comprise particles ofgas-exfoliated vermiculite, eg the layer may comprise particles ofgas-exfoliated vermiculate bonded with the particles of CEV. Thegas-exfoliated vermiculite may be milled to a particle size of less than50 μm. Other possible additives include talc, mica and unexfoliatedvermiculite.

By dry CEV is meant CEV having a moisture content of less than 20% w/w,more preferably, less than 10% w/w, most preferably, less than 5% w/w.

Preferably, the CEV component in the wet dough comprises a mixture ofdried CEV and CEV in a slurry form. However, it is necessary to usesufficient dried CEV to give an acceptable solids content. A high solidscontent in the wet dough assists reduction in skinning in the subsequentdrying process.

Preferably, the dry CEV is prepared by a suitable drying technique.Suitable drying techniques include:

cake drying and pulverising;

film drying and pulverising;

rotary hot air drying;

spray drying;

freeze drying;

pneumatic drying;

fluidised bed drying of partially dried solid; and

vacuum methods including vacuum shelf drying.

Preferably, any of the features or any preferred features of any aspectof the present invention may be combined with the first aspect of thereference to the first aspect in the method of the second aspect shouldbe interpreted accordingly.

Preferably, the hydrolysis resistant polymer is coupled to thevermiculite by coupling agent.

Thus, according to a third aspect of the present invention there isprovide a gasket comprising a sealing layer formed from a resilientmaterial which comprises particles of chemically exfoliated vermiculitebonded together, wherein in the layer also comprises ahydrolysis-resistant polymer coupled to the vermiculite by a couplingagent.

In a gasket according to this aspect of the invention, it is found thatthe layer is more water resistant than a material containing onlyvermiculite and a coupling agent and also more water resistant than amaterial containing only vermiculite and a polymer. Preferably, thesealing layer of the third aspect is in accordance with any of theaspects of the present invention. Accordingly, any of the preferredfeatures of any aspect of the present invention defined herein may becombined with the third aspect of the present invention.

The coupling agent may be a silane, eg a vinyl functional silane such astriethoxy vinyl silane (CH₃CH₂O)₃SiCH═CH₂.

Spirally wound gaskets are well-known and are formed from a metalsupporting strip, conventionally of steel, and a sealing strip formedfrom a resilient material, conventionally expanded graphite (also calledexfoliated graphite). In the formation of conventional spirally woundgaskets, the steel supporting strip is fed onto a mandrel. The steelsupporting strip is welded either to itself to form a closed loop aroundthe mandrel or, alternatively, is welded to an inner ring of the gasketwhich is itself mounted on the mandrel. The mandrel is then rotated todraw further supporting strip on to the mandrel to form a planar spiral.Simultaneously, the sealing strip is drawn between the coils of thesteel strip so that a spiral of the sealing strip is formed interposedbetween the coils of the supporting strip. When the gasket spiral hasbeen completed, the steel supporting strip is welded to itself to form aclosed loop at the outside of the gasket and the gasket is removed fromthe mandrel. Such gaskets are utilised, for example, for forming sealsbetween flanges at the ends of pipes. The supporting strip holds thesealing strip in position and the sealing strip forms a seal between theflanges and between the coils of the supporting strip.

It should be clear, from the above description of how spirally woundgaskets are formed that, the sealing strip thereof must have sufficientstrength and flexibility to enable it to be drawn into the spiral andformed into a gasket without breakage. A sealing strip formed fromexpanded graphite foil, although relatively brittle, does havesufficient strength.

In many cases, it is desirable for a spirally wound gasket to have ahigh degree of heat resistance but, in a conventional gasket, the heatresistance is limited by that of the expanded graphite which is lowerthan is desirable.

As discussed above, although exfoliated vermiculite has excellent heatresistance and a high degree of resilience, strips formed fromexfoliated vermiculite bound with CEV are not suitable for use inspirally wound gaskets because such strips are inherently too brittle toallow formation of the gasket, by the method described above, withoutserious risk of breakage of the strip.

It is a further object of the present invention to provide a spirallywound gasket in which the sealing strip has increased heat resistance.

According to a fourth aspect, the invention provides a gasket comprisinga sealing strip wound into a spiral, wherein the sealing strip comprisesa resilient layer comprising particles of chemically-exfoliatedvermiculite, and a flexible carrier strip to which said layer is bonded.

In a gasket according to the invention, the resilient layer is bonded tothe carrier strip, so that, during winding of the gasket, the strengthof the strip prevents breakage of the resilient material. This enables agasket with increased heat resistance to be formed.

Preferably, the sealing strip of the fourth aspect of the invention maybe in accordance with any of the aspects of the sealing layer inventiondefined herein or any of the preferred features thereof.

The resilient layer may also comprise particles of gas-exfoliatedvermiculite, eg the layer may comprise particles of gas-exfoliatedvermiculite bonded together by particles of CEV. The particles ofgas-exfoliated vermiculite may be milled to a diameter of 50 μm or less.It is also possible for the resilient layer to comprise unexfoliated(intumescent) vermiculite which can, on heating of the gasket, eg insitu, form TEV to swell the resilient layer and, thus improve sealing.

In order to improve the water-resistance of the gasket, the resilientlayer may also comprise a hydrolysis-resistant polymer coupled to thevermiculite. Suitable polymers have been defined with respect to thefirst aspect of the invention above. Suitable agents for coupling thepolymer to the vermiculite are silanes, eg vinyl functional silanes,such as triethoxy vinyl silane (CH₃CH₂O)₃SiCH═CH₂.

Said resilient layer and a further resilient layer may be bonded toopposite sides of the carrier strip. This improves sealing by providingseals on both sides of the carrier strip. However, coating on one sideonly is also possible where the carrier strip is also the supportingstrip as the carrier strip is effectively provided with a sealing layeron both sides due to the spiralling of the carrier strip.

The resilient layer may be bonded to the carrier strip by adhesive butit may be advantageous if it is mechanically bonded.

The carrier strip may be made of fabric, paper, glass tissue or plasticsmaterial but, for high temperature applications, it is preferred if itis made of metal. Where the gasket also comprises a separate supportingstrip so that the carrier strip functions only to enable formation ofthe gasket without breakage of the resilient layer, the carrier stripis, preferably, a thin metal foil, eg of aluminum, nickel or steel.However, it is also possible for the carrier strip to function also asthe supporting strip of the gasket, being made of, eg, stainless steel.The resilient layer may be mechanically bonded to a metal carrier stripby tangs projecting from the carrier strip into the resilient layer. Forexample, a strip of tanged metal and a layer of the resilient materialmay be passed between rollers to press the tangs into the resilientmaterial.

Preferably, a metal carrier strip has end portions which are not bondedto the resilient layer so that these end portions can be welded in theformation of the gasket.

It is a still further object of the present invention to provide agasket comprising a layer of sealing enhancing material which is basedon exfoliated vermiculite, the layer containing a cost-reducing fillerwhich does not significantly reduce the effectiveness of the layer.Preferably, the filler should be halogen-free and sulphur free andshould reduce the possibility of heat damage and corrosion.

Preferably, the gaskets in accordance with any of the aspects of thepresent invention comprise a sealing layer formed from a resilientmaterial which comprises particles of chemically exfoliated vermiculitebonded together, the layer being at least 200 microns in thickness,wherein the layer also comprises 1-90% by weight of a plate-like filler.

Accordingly, in accordance with a fifth aspect of the present inventionthere is provided a gasket comprising a sealing layer formed from aresilient material which comprises particles of chemically-exfoliatedvermiculite bonded together, the layer being at least 200 microns inthickness, wherein the layer also comprises 1-90% by weight of aplate-like filler.

The sealing layer of the fifth aspect may be in accordance with any ofaspects of the invention defined herein or any of the preferred featuresthereof.

In a gasket according to any aspect of the invention, it is found thatthe particles of the plate-like filler tend to orientate themselves intothe plane of the layer and act like a large number of tiny leaf springs,thereby improving sealing.

In accordance with any aspect of the present invention the plate-litefiller may be selected from the group consisting of talc, molybdenumdisulphide, hexagonal boron nitride, soapstone, pyrophyllite, milledthermally exfoliated vermiculite, mica, fluoromica, powdered graphite,glass flake, metal flake, ceramic flake, or kaolinites.

In general, a plate-like filler has an average width of plates of atleast three times the average thickness.

In a gasket according to the fifth aspect of the invention, the layermay comprise 5-80%, eg 40-60%, by weight of the plate-like filler.

One of the desirable properties of a gasket is high stress retention andit has been assumed that the way to achieve high stress retention in agasket with a sealing layer formed from CEV is to compress the layer toconsolidate it to approaching the theoretical density of CEV. Thus, suchsealing layers have previously been formed with a density of 2.0 to 2.4g/cm³. However, such gaskets, although they have low gas permeability,exhibit undesirably low stress retention.

It is a still further object of the present invention to provide agasket comprising a sealing layer based on CEV which has improved stressretention, while retaining low gas permeability.

Preferably, the sealing layer of any of the aspects of the presentinvention has a density in an uncompressed state of less than 1.6 g/cm³.

Accordingly, according to a sixth aspect of the present invention thereis provided a gasket comprising a sealing layer formed from a resilientmaterial which comprises particles of chemically-exfoliated vermiculitebonded together, wherein the sealing layer has a density, in anuncompressed state, of less than 1.6 g/cm³.

In a gasket according to any aspect of the invention, in which thedensity of the sealing layer is much lower than is conventional, it issurprisingly found that stress retention is greatly increased while lowgas permeability is also present.

In a gasket according to any aspect of the invention, the sealing layermay have a density, in an uncompressed state, of less than 1.4 g/cm³,for example the density may be between 0.8 and 1.4 g/cm³.

The sealing layer of the sixth aspect may be in accordance with any ofthe aspects of the invention defined herein or the preferred featuresthereof.

It is a still further object of any aspect of the present invention toprovide a gasket comprising a sealing layer based on exfoliatedvermiculite, which layer comprises a polymeric binder, the layerproviding improved sealing at temperatures at which the binder degrades.

Preferably, the sealing layer of any aspect of the present inventionalso comprises an intumescent material selected so that it expands attemperatures at which said hydrolysis resistant polymer degrades.

Thus, according to a seventh aspect of the present invention there isprovided a gasket comprising a sealing layer formed from a resilientmaterial which comprises exfoliated vermiculite, and a polymeric binder,wherein the layer also comprises an intumescent material selected sothat it expands at temperatures at which said binder degrades.

The sealing layer of the seventh aspect may be in accordance with any ofthe aspects of the invention defined herein or any of the preferredfeatures thereof.

In a gasket according to the invention, at temperatures which cause thebinder to degrade, the intumescent material expands to at leastpartially fill the void left by the binder, thereby helping to maintainsealing.

Preferably, the intumescent material is unexfoliated vermiculitebecause, after exfoliation, it has good heat resistance. Anotherpossibility, is to use partially exfoliated vermiculite, ie vermiculitewhich has been exfoliated at a lower temperature than is normallyrequired to fully exfoliate it. The unexfoliated or partially exfoliatedvermiculite may be treated (by methods which are known per se) to reducethe temperature at which exfoliation occurs, eg the temperature can bereduced to as low as 160° C. Other possible intumescent materialsinclude expandable graphite, sodium silicate, and perlite.

The intumescent material may form up to 50% by weight of the layer butup to 20% is preferred.

There now follows a detailed description of illustrative examplesaccording to the different aspects of the invention.

Tanged stainless steel sheet was first prepared. This sheet was 100 μmin thickness. The sheet was tanged by perforating it with square holes,each hole being 1.5 mm square and the hole centre-spacing being 3 mm.Half the holes were perforated by passing a tool through the sheet in afirst direction and the remaining half, which alternated with thefirst-mentioned half, were perforated by passing a tool through thesheet in the opposite direction. The edges of the holes, thus, formedtangs projecting from the sheet in opposite directions. The tangsprojected by about 1 mm.

The manufacture of laboratory samples was achieved using methodsrepresentative of the techniques available in a factory involved in theproduction of gasket materials.

Mixing of the vermiculite dough was carried out in the following manner.

Various forms of readily available mixers have been found to besatisfactory in the preparation of the required dough. Typical examplesare Z blade mixers, Hobart type mixers and, for small scale mixers,Kenwood Chef type mixers.

About half of the dry vermiculite was added to the pan of whatever mixerwas to be used and to it was added all the CEV dispersion. This was thenmixed for three minutes and the rest of the dry material was added tothe pan and the mixing continued for a further five minutes. If a silanecoupling agent was being used it was then added and mixing continued fora further three minutes. At this time the rubber was added to the mix asa solution in toluene, made as indicated below, and the mixing wascontinued for a further five minutes after which the dough was removedfrom the mixer and stored in a plastic bag.

The CEV used was W R Grace's HTS dispersion which is approximately 15%solids. The dry CEV used was W R Grace's “Microlite Powder”. The rubberused in these examples was either nitrile rubber N36C80 from Zeon orsilicone SR224 from General Electric. The silane used was vinylsilane—the preferred coupling agents are vinylalkoxysilane such as“Silquest A151” from OSi specialities.

The aluminate examples were modified in accordance with GB 2 217 742 andfor these a post sheet making immersion was sometimes used to addpolymer to the mix which otherwise contained none.

The silane was added to the stated weight of the total vermiculitesolids.

Unless otherwise stated the dough mixed was formed on to a core oftanged stainless steel of 0.1 m thickness.

The forming on to the core carried out by a simple calendering operationbut other techniques such as spreading and pultrusion could be used.

Materials were dried at a temperature in the range of about 80 to 120°C. and then cured at the temperature appropriate for the cure systemdisclosed.

The NBR rubber solution was made as given in Example 1 below.

EXAMPLE 1

An aqueous slurry (15% solids) was obtained containing about 0.741 kg ofCEV particles (the slurry was obtained from Grace Construction Productsand is designated “Microlite HTS”). The slurry was approximately 15%solids. To this slurry was added 0.074 kg of particles of dried CEVhaving particle size about 45 μm obtained from Grace ConstructionProducts Limited and designated “Micolite Powder”. To this, was added0.185 kg of Dupre Superfine TEV. This gave a paste having approximately37% solids. To this paste was added 3.7 g of a coupling agent (a vinylfunctional silane called “Silquest A-151” obtainable from OSiSpecialities) and further mixing was carried out.

Next, a hydrolysis-resistant polymer/solvent mixture was prepared. Thismixture was 50 g of solid nitrile butadiene rubber (Nippon Zeon N36C80),250 g of toluene, and 3.1 g of a curing agent (“Dicup 40”,dicumylperoxide). 111 g of this mixture (ie 18.5 g of rubber) was addedto the above-mentioned paste and mixing was carried out. This gave apaste with approximately 5% rubber content.

Next, the paste (including the polymer/solvent mixture) was spread overone side of the metal sheet mentioned above. The sheet was then passedbetween calendering rollers (using release paper to prevent the pastesticking to the rollers) and was dried. Further paste was then spreadover the other side of the metal sheet and the calendering and dryingwas repeated. The sheet was then pressed to densify the resilientmaterial which formed layers approximately 0.75 mm thick on both sidesof the metal. Then it was heated to peroxide cure the rubber at 180° C.for 15 minutes.

The completed gasket had two sealing layers formed from a resilientmaterial. The resilient material comprised particles of CEV bondedtogether, and coupled to the nitrile butadiene rubber by the silane. Thegasket was tested to determine its water resistance by boiling in waterfor 5 hours. The gasket retained its integrity.

EXAMPLE 2

An aqueous slurry (15% solids was obtained containing about 0.471 Kg ofCEV particles (the slurry was obtained from Grace Construction ProductsLimited and is designated “Microlite HTS”). The slurry was approximately15% solids. To this slurry was added 0.529 Kg of particles of dried CEVhaving particle size about 45 μm obtained from Grave ConstructionProducts Limited and designated “Microlite Powder”. This gave a pastehaving approximately 60% solids. To this paste was added 6 g of acoupling agent (a vinyl functional silane called “Silquest A-151”obtainable from OSi Specialities) and further mixing was carried out.

Next, a rubber/solvent mixture was prepared. This mixture was 50 g ofsolid nitrile butadiene rubber (Nippon Zeon N36C80), 250 g of toluene,and 3.1 g of a curing agent (“Dicup 40”, dicumylperoxide). 90.9 g ofthis mixture was added to the above-mentioned paste and mixing wascarried out. This gave a paste with approximately 2.5% rubber content.

Next, the paste (including the rubber/solvent mixture) was spread overone side of the metal sheet mentioned above. The sheet was then passedbetween calendering rollers (using release paper to prevent the pastefrom sticking to the rollers) and was dried. Further paste was thenspread over the other side of the metal sheet and the calendering anddrying was prepared. The sheet was then pressed to densify the resilientmaterial which formed layers approximately 1.4 mm thick on both sides ofthe metal. It was then heated to peroxide cure the rubber at 180° C. for15 minutes.

The metal sheet was then slit into strips 7 mm wide on a conventionalslitting machine and these strips, thereby forming a metal carrier stripwith resilient layers bonded to both sides thereof. The strips werewound into a spiral gasket by a conventional winding machine. Thecompleted gasket had a spiral of stainless steel strip, acting as asupporting strip of the gasket, with two resilient layers betweenadjacent coils of the steel.

The gasket made according to the illustrative method was heated to 450°C. and held at that temperature for 8 hours. After returning to ambienttemperature, the gasket was subjected to a standard pressure test and noleakage was observed.

EXAMPLE 3

The aqueous slurry was prepared in accordance with example 1 aboveexcept that only 0.166 kg of Duprey Superfine TEV was added. To this wasadded 19 g unexfoliated vermiculite. ie intumescent vermiculite. Thisgave a paste having approximately 37% solids. To this paste was added 4g of a coupling agent (a vinyl functional silane called “Silquest A-151”obtainable from OSi Specialities) and a further mixing was carried out.

The hydrolysis-resistant polymer/solvent mixture was prepared as perexample 1. The layers contained approximately 5% by weight ofintumescent vermiculite.

The completed gasket of the first illustrated example had two sealinglayers formed from a resilient material. The resilient materialcomprised particles of CEV bonded together, and coupled to the nitrilebutadiene rubber by the silane. The material also comprised particles ofintumescent unexfoliated vermiculite. The gasket was tested to determineits water resistance by boiling in water for 5 hours. The gasketretained its integrity. The gasket was also tested at 450° C. (atemperature which would be expected to de-grade the rubber and allowleakage) and no leakage was observed.

EXAMPLE 4

The third example was repeated except that the TEV added to the slurrywas omitted and replaced by further unexfoliated vermiculite, ie 0.185kg of unexfoliated vermiculite was added. This gave layers in the gasketcontaining 47.0% by weight of intumescent unexfoliated vermiculite.

EXAMPLE 5

The third example was repeated except that 0.181 kg of TEV was added(instead of 0.166 kg) and 4 g of unexfoliated vermiculite was added(instead of 19 g). This gave layers containing 1.1% by weight ofintumescent unexfoliated vermiculite.

EXAMPLE 6

An aqueous slurry (15% solids) was obtained containing about 0.741 kg ofCEV particles (the slurry was obtained from Grace Construction Productsand is designated “Microlite HTS”). To this slurry was added 0.074 kg ofparticles of dried CEV having particle size about 45 microns obtainedfrom Grace Construction Products and designated “Microlite Powder”. Tothis, was added 0.148 kg of Dupre Superfine TEV. To this was added 37 gof Molybdenum disulphide (99%<2 μm powder, ex Aldrich Chemicals). Thisgave a paste having approximately 37% solids. The mineral content of thepaste was 50% CEV and 40% TEV. To this paste was added 3.7 g of acoupling agent (a vinyl functional silane called “Silquest A-151”obtainable from OSi Specialities) and further mixing was carried out.

The hydrolysis-resistant polymer was prepared in accordance with example1 and similarly the spreading calendering, and drying was repeated asdescribed in example 1.

The completed gasket had two sealing layers formed from a resilientmaterial. The resilient material comprised particles of CEV bondedtogether, and coupled to the nitrile butadiene rubber by the silane. Thegasket was tested to determine its water resistance by boiling in waterfor 5 hours. The gasket retained its integrity.

EXAMPLE 7

Example 6 was repeated except that 37 g of talc (ex Norwegian Talc (UK)Ltd, trade IT300) was added instead of the molybdenum disulphide.

EXAMPLE 8

Example 6 was repeated except that 37 g of powdered graphite (ex DavidHart Ltd) was added instead of molybdenum disulphide.

EXAMPLE 9

Example 8 was repeated except that 185 g of powdered graphite was added,(instead of TEV) giving equal proportions of graphite and CEV.

EXAMPLE 10

Example 9 was repeated except that 185 g of mica was added instead ofgraphite.

EXAMPLE 11

0.659 kg of an aqueous slurry (15% solids) was obtained containing about99 kg of CEV particles (the slurry was obtained from Grace ConstructionProducts and is designated “Microlite HTS”). To this slurry was added0.121 kg of particles of dried CEV having particle size about 45 μmobtained from Grace Construction Products and designated “MicrolitePowder”. To this, was added 0.220 kg of Dupre Superfine TEV. This gave apaste having approximately 44% solids. To this paste was added 4 g of acoupling agent (a vinyl functional silane called “Silquest A-151”obtainable from OSi Specialities) and further mixing was carried out.

The hydrolysis-resistant polymer was prepared in accordance withexample 1. 132 g of this mixture (21.9 g of rubber) was added to theabove mentioned paste and mixing was carried out. This gave a paste withapproximately 5% rubber content in the dry sealing layer.

Next, the paste (including the polymer/solvent mixture) was spread overone side of the metal sheet mentioned above. The sheet was then passedbetween calendering rollers so that the thickness of the layer of pastewas 2.1 mm. The paste was then dried which reduced its thickness of 1.6mm. The same quantity of paste was then spread over the other side ofthe metal sheet and the calendering and drying was repeated. The layersof vermiculite were then pressed to consolidate the material to adensity of 0.89 g/cm³ which formed sealing layers approximately 1 mmthick on both sides of the metal sheet. Then, it was heated to peroxidecure the rubber. A gasket was then cut out from the sheet. The gasketwas in the form of a ring, having an internal diameter of 55 mm and anexternal diameter of 75 mm.

The completed gasket obtained by the illustrative example had twosealing layers formed from a resilient material. The resilient materialcomprised particles of CEV bonded together, and coupled to the nitrilebutadiene rubber by the silane.

The gasket obtained by the illustrative example was tested to determineits stress resolution. The gasket was placed in a test rig as describedin the appendix to British Standard 7531 and stressed to 40 MPa. Thegasket was heated to 300° C. over a period of 1 hour and then held atthat temperature for 16 hours. The stress retention was the measured andfound to be 30 MPa. The gasket obtained by the illustrative example wasalso found to have a low gas permeability properties (leakage of only0.02 ml/minute in the test described in DIN 3754).

As a comparative example, example 11 was repeated except that the pastewas spread on to the metal sheet to a thickness of 3.3 mm which dried toa thickness of 2.4 mm. The layers were pressed to a thickness of 1 mmgiving them a density of 1.66 g/cm³. The gasket obtained by thecomparative example was tested by the method described above todetermine its stress retention, the result being 16.4 MPa. The gasketobtained by the comparative example was also found to have acceptablegas permeability properties (leakage of 0.12 ml/minute in the DIN test).

Example 12 98% vermiculite 1% silicone resin 1% vinyl alkoxy (comprising50% (SR 224 available silane (Silquest CEV and 50% from GE) A-151) TEVExample 13 89% vermiculite 10% silicone resin 1% vinyl alkoxy(comprising 50% (SR 224 available silane (Silquest CEV and 50% from GE)A-151) TEV) Example 14 94% vermiculite 1% coupling agent 5%acrylonitrile (comprising (Silquest A-151) butadiene rubber 30% CEV (exZeon) 20% FPSV (TEV milled) 50% TEV) Example 15 94% vermiculite 1%coupling aqent 5% acrylonitrile (comprising 50% (Silquest A-151)butadiene rubber FPSV (TEV (ex Zeon) milled) 50% TEV) Example 16 89%vermiculite 1% coupling agent 10% acrylonitrile (comprising (SilquestA-151) butadiene rubber 50% FPSV (TEV (ex Zeon) milled) 50% TEV) Example17 91.5% 1% coupling agent 7.5% vermiculite (Silquest A-151)acrylonitrile (comprising 50% butadiene rubber FPSV (TEV (ex Zeon)milled) 50% TEV) Example 18 94% vermiculite 1% coupling agent 5%acrylonitrile (comprising (Silquest A-151) butadiene rubber 50% CEV (exZeon) 50% TEV) Example 19 94% vermiculite 1% coupling aqent 5% silicone(comprising (Silquest A-151) resin (SR 224 35% CEV from GE) 65% TEV)Example 20 94% vermiculite 1% coupling agent 5% acroylontirle(comprising (Silquest A-151) butadiene rubber 35% CEV (ex Zeon) 65% TEV)Example 21 90% vermiculite 5% coupling agent 5% silicone resin(comprising (Silquest A-151) (SR 224 from 50% CEV GE) 50% TEV) Example22 98% vermiculite 1% coupling agent 1% silicone resin (comprising(Silquest A-151) (SR 224 from 50% CEV GE) 50% TEV Example 23 96%vermiculite 2% coupling agent 2% silicone resin (comprising (SilquestA-151) (SR 224 from 50% CEV GE) 50% TEV) Example 24 94.5% 0.5% coupling5% silicone resin vermiculite agent (SR 224 from (comprising 50%(Silquest A-151) GE) CEV 50% TEV) Example 25 94% vermiculite 1% couplingagent 5% acrylonitrile (comprising (Silquest A-151) butadiene rubber 30%CEV (ex Zeon) 70% TEV) Example 26 94% vermiculite 1% coupling agent 5%acrylonitrile (comprising (Silquest A-151) butadiene rubber 50% CEV (exZeon) 50% TEV) Example 27 94% vermiculite 1% coupling agent 5%acrylonitrile (comprising (Silquest A-151) butadiene rubber 50% CEV (exZeon) 50% TEV) Example 28 94% vermiculite 1% coupling agent 5%acrylonitrile (comprising (Silquest A-151) butadiene rubber 50% CEV (exZeon) 50% TEV) Example 29 50% CEV Soak in NaOH 50% TEV stabilised NaA10₂solution Example 30 50% CEV Soak in NaOH Soak in 36% 50% TEV stabilisedNaA10₂ solution of solution silicone (SR224) in toluene

As can be seen from comparative table 1, the higher the polymer level,the lower the stress retention but the less permeable the facing and thelower the polymer level, the higher the stress retention and the higherthe permeability.

Examples 14-18 make a comparison of the effect of substituting TEV forCEV in the sealing layer. The examples are shown above.

As can be seen from a comparison of example 18 and example 14 thereplacement of CEV with FPSV results in an increase in the permeabilityof the sealing layer which is undesirable.

As can be seen from table 4, the change in the level of silane haslittle effect on gas permeability but does cause a loss in stressretention at levels as high as 5% compared with a level of 0.5%.

As can be further seen from table 4, Example 22 and Example 23 both showimproved stress retention owing to the lower levels of siliconeelastomer used in the formulation. The highest stress retention is shownby Example 22 which has a lower level of both rubber and silane comparedwith Example 23.

A conversion of the core types in table 5 shows that the tanged metalcore has reduced gas permeability compared to the glass tissue and wovenwire gauze when the latter are not initially treated with suitablefiller body.

Examples 29 and 30 demonstrate the aluminate route of waterproofingdescribed in GB 2217742 (and EP 0339343). The examples were manufacturedusing the materials used in previous examples.

Example 30 differs from Example 29 in that the sample has been soaked insilicone elastomer (SR224 ex GE silicones). Without the siliconeelastomer soak the material was brittle and very difficult to cut intogaskets as well as having poor gas sealing properties.

The aluminate waterproofing was carried out after the consolidationstage. The sheet was soaked in a sodium hydroxide stabilised sodiumaluminate solution (82 g sodium aluminate, 14 g sodium hydroxide in aliter of water) for 30 minutes. It was then rinsed in water and dried, asubsequent soak (15 minutes) in silicone solution (18% resin in toluene)was also employed to reduce friability and improve sealing.

In the above examples it is clear that only relatively low levels ofhydrolysis resistant polymer are required with higher levels of CEV.This surprisingly prevents reduction in stress retention whilst alsosurprisingly maintaining low permeability and hydrolysis resistance inthe sealing layer.

TABLE 1 Example 12 Example 13 Thickness t mm 2.20 1.635 Facing densitygm/cm³ 1.69 1.82 ASTM compression % — 18.6 ASTM recovery % — 10 BSStress Retention 26.6 8.8 MPa DIN Gas Leakage 2.0 0.02 mL/min

TABLE 2 Example Example Example Example Example 14 15 16 17 18 Thickness2.42 2.55 2.59 2.66 2.35 mm Facing den- 1.68 1.28 1.09 1.04 1.71 sitygm/cm³ ASTM K% 24.9 27.8 35.0 47.3 22.8 ASTM rec % 14 20 15 7.5 16 BSS/R MPa 18.0 20.6 18.2 18.8 13.3 DIN G/L 2.1 >20 >20 0.03 0.2 mL/min

TABLE 3 Example 19 Example 20 Thickness mm 1.46 1.35 Facing Densitygm/cm³ 1.76 1.66 ASTM Compression % 15.2 21.3 ASTM Recovery % 20 10 BSStress Retention MPa 21.1 27.6 DIN G/L mL/min 0.0006 0.01

TABLE 4 Example 21 Example 22 Example 23 Example 24 Thickness mm 1.891.40 1.50 1.52 Facing Density 1.89 2.05 1.98 — gm/cm³ BS S/R MPa 12.627.7 19.9 7.6 DIN G/L mL/ 0.07 0.02 0.22 0.09 min

TABLE 5 Example 25 Example 26 Example 27 Example 28 Thickness mm 2.3 2.21.75 2.3 Facing Density 1.42 1.16 1.51 1.42 gm/cm³ ASTM com- 26.4 38.530.9 19.4 pression % ASTM rec % 15 12 11 26 BS S/R MPa 19.2 25.7 24.522.0 DIN G/L mL/ >20 0.21 >20 >20 min Core types woven wire tanged metalGlass tissue woven wire gauze gauze

TABLE 6 Example 29 Example 30 Thickness mm 2.0 2.0 Facing Density gm/cm³1.8 1.8 ASTM compression % N/A 29.5 ASTM rec % N/A 11 BS S/R MPa N/A21.7 DIN G/L mL/min >20 9.1

The reader's attention is directed to all papers and documents which arefiled concurrently with or previous to this specification in connectionwith this application and which are open to public inspection with thisspecification, and the contents of all such papers and documents areincorporated herein by reference.

All of these features disclosed in this specification (including anyaccompanying claims, abstract and drawings), and/or all of the steps ofany method or process so disclosed, may be combined in any combination,except combinations where at least some of such features and/or stepsare mutually exclusive.

Each feature disclosed in this specification (including any accompanyingclaims, abstract and drawings), may be replaced by alternative featuresserving the same, equivalent or similar purpose, unless expressly statedotherwise. Thus, unless expressly stated otherwise, each featuredisclosed in one example only of a generic series of equivalent orsimilar features.

The invention is not restricted to the details of the foregoingembodiment(s). The invention extends to any novel one, or any novelcombination, of the features disclosed in this specification (includingany accompanying claims, abstract and drawings), or to any novel one, orany novel combination, of the steps of any method or process sodisclosed.

What is claimed is:
 1. A gasket comprising a sealing layer and a supportlayer the sealing layer being formed from a resilient material whichcomprises a chemically exfoliated vermiculite (CEV) component in aproportion of at least 25% w/w of the sealing layer, said CEV componentbeing at least partially derived from dry CEV, and a hydrolysisresistant polymer to improve the water resistance of said sealing layerwherein the proportion of said polymer does not exceed 20% of thesealing layer, and wherein said chemically exfoliated vermiculitecomponent includes sufficient dry CEV to provide a wet sealing layerdough with a reduced water content which is capable of being driedbefore substantial skinning has occurred.
 2. A gasket comprising asealing layer and a support layer the sealing layer being formed from aresilient material which comprises a chemically exfoliated vermiculite(CEV) component in a proportion of at least 25% w/w of the sealinglayer, said CEV component being at least partially derived from dry CEV,and a hydrolysis resistant polymer to improve the water resistance ofsaid sealing layer wherein the proportion of said polymer does notexceed 20% of the sealing layer, wherein the level of CEV is within therange of 25% to 80% w/w of said sealing layer, and wherein saidchemically exfoliated vermiculite component includes sufficient dry CEVto provide a wet sealing layer dough with a reduced water content whichis capable of being dried before substantial skinning has occurred.
 3. Agasket comprising a sealing layer and a support layer the sealing layerbeing formed from a resilient material which comprises a chemicallyexfoliated vermiculite (CEV) component in a proportion of at least 25%w/w of the sealing layer, said CEV component being at least partiallyderived from dry CEV, and a hydrolysis resistant polymer to improve thewater resistance of said sealing layer wherein the proportion of saidpolymer does not exceed 20% of the sealing layer, wherein the proportionof said polymer is less than 15% w/w of said sealing layer, and whereinsaid chemically exfoliated vermiculite component includes sufficient dryCEV to provide a wet sealing layer dough with a reduced water contentwhich is capable of being dried before substantial skinning hasoccurred.
 4. A gasket comprising a sealing layer and a support layer thesealing layer being formed from a resilient material which comprises achemically exfoliated vermiculite (CEV) component in a proportion of atleast 25% w/w of the sealing layer, said CEV component being at leastpartially derived from dry CEV, and a hydrolysis resistant polymer toimprove the water resistance of said sealing layer wherein theproportion of said polymer does not exceed 20% of the sealing layer,wherein the level of CEV is within the range of 25% to 80% w/w of saidsealing layer, wherein the proportion of said polymer is less than 15%w/w of said sealing layer, and wherein said chemically exfoliatedvermiculite component includes sufficient dry CEV to provide a wetsealing layer dough with a reduced water content which is capable ofbeing dried before substantial skinning has occurred.
 5. The gasket ofclaim 1, a gasket comprising a sealing layer and a support layer thesealing layer being formed from a resilient material which comprises achemically exfoliated vermiculite (CEV) component in a proportion of atleast 25% w/w of the sealing layer, said CEV component being at leastpartially derived from dry CEV, and a hydrolysis resistant polymer toimprove the water resistance of said sealing layer wherein theproportion of said polymer does not exceed 20% of the sealing layerwherein said chemically exfoliated vermiculite component includessufficient dry CEV to provide a wet sealing layer dough with a reducedwater content which is capable of being dried before substantialskinning has occurred, wherein a suitable hydrolysis resistant polymeris selected from: nitrile butadiene rubbers, styrene butadiene rubbers,natural rubber, butyl rubber, siloxanes and ethylene-propyldienepolymers or other diene based polymers.
 6. The gasket of claim 1, agasket comprising a sealing layer and a support layer the sealing layerbeing formed from a resilient material which comprises a chemicallyexfoliated vermiculite (CEV) component in a proportion of at least 25%w/w of the sealing layer, said CEV component being at least partiallyderived from dry CEV, and a hydrolysis resistant polymer to improve thewater resistance of said sealing layer wherein the proportion of saidpolymer does not exceed 20% of the sealing layer wherein said chemicallyexfoliated vermiculite component includes sufficient dry CEV to providea wet sealing layer dough with a reduced water content which is capableof being dried before substantial skinning has occurred, wherein saidsealing layer is water resistant to the extent that it can withstandsubmersion in boiling water for a period in excess of two hours.
 7. Thegasket of claim 1, a gasket comprising a sealing layer and a supportlayer the sealing layer being formed from a resilient material whichcomprises a chemically exfoliated vermiculite (CEV) component in aproportion of at least 25% w/w of the sealing layer, said CEV componentbeing at least partially derived from dry CEV, and a hydrolysisresistant polymer to improve the water resistance of said sealing layerwherein the proportion of said polymer does not exceed 20% of thesealing layer wherein said chemically exfoliated vermiculite componentincludes sufficient dry CEV to provide a wet sealing layer dough with areduced water content which is capable of being dried before substantialskinning has occurred, wherein said gasket is substantially ambientwater resistant for a period in excess of 20 hours.
 8. A method ofmanufacturing a gasket comprising the steps of: applying a wet sealinglayer dough formed from a resilient material which comprises achemically exfoliated vermiculite (CEV) component in a proportion of atleast 25% w/w of said sealing layer, said CEV component being at leastpartially derived from dry CEV, and a hydrolysis resistant polymerwherein the proportion of said polymer does not exceed 20% w/w of saidsealing layer; and drying said wet sealing layer dough on said supportmaterial; wherein the solids content of said wet sealing layer doughprior to said drying step is in the range of 30% through 80% w/w of saiddough material.
 9. The method of claim 8, wherein said CEV is mixed witha suitable filling agent.
 10. The method of claim 8, wherein a fillingagent comprises less than 75% of said sealing layer.
 11. The method ofclaim 9, wherein said filing agent comprises less than 75% of saidsealing layer.
 12. The method of claim 8, wherein said wet sealing layerdough is dried within four hours per millimeter thickness of a drysealing layer per side.
 13. The method of claim 8, wherein said wetsealing layer dough is dried within four hours per millimeter thicknessof a dry sealing layer per side.
 14. The method of claim 8, wherein saiddough is dried between 80 through 135 degrees Celsius.
 15. The method ofclaim 9, wherein said dough is dried between 80 through 135 degreesCelsius.
 16. The method of claim 12, wherein said dough is dried between80 through 135 degrees Celsius.
 17. The method of claim 8, wherein therelative ratio of non-dry CEV to dry CEV in the total CEV component isbetween 0.01:1 and 20:1.
 18. The method of claim 9, wherein the relativeratio of non-dry CEV to dry CEV in the total CEV component is between0.01:1 and 20:1.
 19. The method of claim 12, wherein the relative ratioof non-dry CEV to dry CEV in the total CEV component is between 0.01:1and 20:1.
 20. The method of claim 17, wherein said dry CEV component isproduced by a drying technique selected from the group of: cake dryingand pulverizing; film drying and pulverizing; rotary hot air drying;spray drying; pneumatic drying; fluidised bed drying of partially driedsolid; or vacuumed dried.
 21. The method of claim 18, wherein said dryCEV component is produced by a drying technique selected from the groupof: cake drying and pulverizing; film drying and pulverizing; rotary hotair drying; spray drying; pneumatic drying; fluidised bed drying ofpartially dried solid; or vacuumed dried.
 22. The method of claim 19,wherein said dry CEV component is produced by a drying techniqueselected from the group of: cake drying and pulverizing; film drying andpulverizing; rotary hot air drying; spray drying; pneumatic drying;fluidised bed drying of partially dried solid; or vacuumed dried. 23.The method of claim 17, wherein said dry CEV has a moisture content ofless than 20%.
 24. The method of claim 18, wherein said dry CEV has amoisture content of less than 20%.
 25. The method of claim 19, whereinsaid dry CEV has a moisture content of less than 20%.
 26. The method ofclaim 8, wherein the CEV component in said wet dough comprises a mixtureof dry CEV and CEV in a slurry form.
 27. The method of claim 14, whereinthe CEV component in said wet dough comprises a mixture of dry CEV andCEV in a slurry form.
 28. The method of claim 8, wherein a hydrolysisresistant polymer is coupled to the vermiculite by a coupling agent. 29.The method of claim 10, wherein a hydrolysis resistant polymer iscoupled to the vermiculite by a coupling agent.
 30. The method of claim11, wherein a hydrolysis resistant polymer is coupled to the vermiculiteby a coupling agent.